Thin film deposition for semiconductor device fabrication is usually carried out through a gas phase process, such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD). In such a process a chemical precursor in liquid form is first vaporized to generate vapor with a carrier gas to form a vapor/gas mixture, which then flows into a deposition chamber to create a thin film on a substrate.
The vapor generating device is usually made of metal and held at an elevated temperature to generate vapor with the desired vapor pressure for the process. At a sufficiently high temperature, the metal surface in contact with the precursor will cause it to thermally decompose forming undesirable by-products and particulate contaminants suspended in the vapor/gas mixture. When the mixture flows into the deposition chamber to form thin films on a substrate, the contaminant particles will deposit on the substrate to form defective films. To reduce particulate contamination a filter can be placed in the vapor/gas stream to remove suspended particles prior to its entry into the deposition chamber.